Characterization of the rheological behavior of a paraffin-based phase change material under steady and oscillatory shear

Solid-liquid phase change materials (PCMs) behavior has been extensively discussed through a set of numerical and experimental investigations. In the current numerical models, natural convection dominated melting is often neglected due to a lack of experiments aiming to characterize the PCM behavior during the melting state. However, it was observed that ignoring this phenomenon causes a large difference between numerical results and experimental data. Hence, natural convection has to be accounted in order to correctly describe the physics encounter in the phase change, especially during melting process. Since natural convection phenomenon depends on the PCM viscosity, the rheological behavior of PCMs should be evaluated properly. In this study, the rheology of RT25, one of the frequently used phase change materials in domestic comfort services, has been described using a Kinexus Lab Rotational Rheometer. Both rotational and oscillatory methods have been used to measure the zero-shear viscosity and the dynamic viscosity which are important parameters of CFD simulations. The Newtonian behavior of RT25 was also demonstrated through dynamic frequency sweep measurements. Moreover, influence of several parameters on the rheological properties has been analyzed.

Automated summary

Research on solid-liquid phase change materials indicates that natural convection must be considered in numerical models to accurately describe the phase change process, especially during melting. The viscosity of PCMs affects natural convection, so the rheological behavior of PCMs should be properly evaluated.